The invention relates to methods for coating the interior surface of tubular structures having high aspect ratios and to tubular structures produced by such methods.
Deposition of coatings onto the interior surface of tubular structures is needed for various applications, including, but not necessarily limited to gun barrels, automotive cylinder bores, and tubes for special applications.
Tubes with relatively large diameters have been successfully coated using known methods. However, as the diameter of the tube becomes smaller and smaller, it becomes more and more difficult to deposit a substantially uniform coating over the entire interior surface. Most methods simply do not succeed if the aspect ratio (length-to-diameter ratio) of the tube is high.
Effective and economical methods are needed to form substantially uniform coatings on interior surfaces of tubes with a high aspect ratio.
The invention provides a method for substantially uniformly coating the interior surface of a tubular structure. The invention also provides a method for coating the interior surface of a tubular structure having a high aspect ratio. The method comprises: inducing a magnetic field having a given magnitude around a circumference along a length of said tubular structure; applying a bias at a given voltage to said tubular structure; and, exposing said interior surface to a gaseous precursor material under conditions effective to convert a quantity of said gaseous precursor material to ionized gaseous precursor material, said given magnitude and said given voltage being effective to deposit said ionized gaseous precursor material onto said interior surface and to convert said ionized gaseous precursor material to a substantially uniform coating on said interior surface. More preferably: the tubular structure has an aspect ratio of at least about 3 or more, even more preferably 6 or more; the conditions comprise an operating pressure of at least about 10xe2x88x923 torr; the bias and the magnetic field generate a glow discharge from said gaseous precursor material that is effective to convert said quantity of gaseous precursor material to the ionized gaseous precursor material; and, the voltage is from about 0.2 kV to about 20 kV.
In a preferred embodiment, the invention provides a method for substantially uniformly coating an interior surface of a tubular structure with amorphous carbon, said method comprising: inducing a magnetic field having a given magnitude around a circumference along a length of said tubular structure; applying a bias at a given voltage to said tubular structure; and, exposing said interior surface to a carbonaceous precursor material under conditions effective to convert a quantity of said carbonaceous precursor material to ionized carbonaceous precursor material, said given magnitude and said given voltage being effective to deposit said ionized carbonaceous precursor material onto said interior surface and to convert said ionized carbonaceous precursor material to a substantially uniform coating comprising amorphous carbon on said interior surface.
In another preferred embodiment, the invention provides a method for substantially uniformly coating an interior surface of a tubular structure with a ceramic, said method comprising: inducing a magnetic field having a given magnitude around a circumference along a length of said tubular structure; applying a bias at a given voltage to said tubular structure; and, exposing said interior surface to a gaseous organometallic precursor material under conditions effective to convert a quantity of said gaseous organometallic precursor material to ionized gaseous organometallic precursor material, said given magnitude and given voltage being effective to deposit said ionized organometallic precursor material onto said interior surface and to convert said ionized organometallic precursor material to a substantially uniform ceramic coating on said interior surface.
In yet another aspect, the invention provides a tubular structure having an aspect ratio of at least about 3 and comprises an interior surface, said interior surface comprising a substantially uniform coating generated from a gaseous precursor material. In a preferred embodiment, the interior surface comprises a substantially uniform amorphous carbon coating. In another preferred embodiment, the tubular structure has an aspect ratio of about 6 or more.